Alkanes AS Flashcards
What are alkanes?
Saturated hydrocarbons with the general formula CₙH₂ₙ₊₂.
What is petroleum?
A mixture mainly consisting of alkane hydrocarbons.
How is crude oil separated?
Crude oil is vaporized and fed through a column that is hotter at the bottom and cooler at the top, allowing fractions to be collected based on boiling points.
What is thermal cracking?
A process that takes place at high temperatures (up to 1000°C) and pressures (up to 70 atm) to produce alkenes from long-chain alkanes.
What is catalytic cracking?
A process that occurs at around 500°C and slight pressure in the presence of a zeolite catalyst, mainly producing motor fuels and aromatic hydrocarbons.
Why do alkanes have specific boiling points?
Their boiling points depend on chain length and branching; longer chains have more Van der Waals forces, leading to higher boiling points.
What is the equation for complete combustion of alkanes?
A: CₙH₂ₙ₊₂ + O₂ → CO₂ + H₂O.
What is the equation for incomplete combustion of alkanes?
CₙH₂ₙ₊₂ + O₂ → CO + H₂O.
What are the issues with CO₂?
It is a greenhouse gas that contributes to global warming; solutions include burning less fossil fuel.
What are the problems associated with CO?
Carbon monoxide is toxic; ensure a good supply of air/oxygen during combustion to minimize this.
What are the problems caused by soot?
Soot can blacken buildings and contribute to global dimming; solutions include ensuring adequate air supply during combustion.
What problems does sulfur dioxide cause?
It leads to acid rain, damaging trees, buildings, and aquatic life; solutions include removing sulfur from fuels or desulfurizing flue gases.
How are nitrogen oxides formed?
Through the reaction of nitrogen and oxygen at high temperatures, often in engines; they also contribute to acid rain.
What is flue gas desulfurization?
A process using alkaline slurry (e.g., calcium carbonate) to remove SO₂ from flue gases, forming harmless calcium sulfate.
What is a free radical?
A highly reactive particle with an unpaired electron, formed when a covalent bond splits.
How is ozone formed in the stratosphere?
UV radiation splits oxygen molecules into free radicals, which react with other oxygen molecules to form O₃.
What are CFCs and why are they banned?
CFCs are inert halogenoalkanes that deplete the ozone layer; they were banned due to their harmful environmental effects.
What are some alternatives to CFCs?
Hydrofluorocarbons (HFCs) and hydrocarbons are safer substitutes now used in refrigeration and aerosol propellants.
What is a halogenoalkane?
A halogenoalkane is an alkane with at least one halogen atom in place of a hydrogen atom.
What are some common uses of halogenoalkanes?
Halogenoalkanes are used as solvents, pharmaceuticals, refrigerators, and propellants.
What is the general formula for mono-substituted halogenoalkanes?
CnH2n+1X, where X is a halogen.
Why is the carbon-halogen bond in a halogenoalkane polar?
Halogens are much more electronegative than carbon, making the carbon atom electron-deficient and prone to attack by nucleophiles.
What are nucleophiles?
Nucleophiles are electron-pair donors that attack electron-deficient carbon atoms. Examples include OH-, CN-, and NH3.
What occurs during the hydrolysis of halogenoalkanes?
When halogenoalkanes react with an aqueous solution of warm hydroxide ions (OH-) and water, they produce an alcohol and a halide ion.
What is the role of hydroxide ions in the hydrolysis of halogenoalkanes?
Hydroxide ions (OH-) donate lone pairs to the electron-deficient carbon, leading to the formation of a covalent bond and the breaking of the carbon-halogen bond.
What is formed when halogenoalkanes react with ethanolic potassium cyanide (KCN)?
A nitrile is formed.
What is the result of reacting a halogenoalkane with excess ethanolic ammonia?
An amine is formed.
What determines the rate of hydrolysis of halogenoalkanes?
The strength of the C-Halogen bond. The C-F bond is the strongest, so fluoroalkanes react slower, while the C-I bond is the weakest, so iodoalkanes react faster.
What type of reaction occurs when halogenoalkanes react with hydroxide ions dissolved in ethanol?
An elimination reaction, forming an alkene.
What are the main mechanisms for halogenoalkane reactions based on their structure?
- Primary Haloalkanes: Mainly undergo nucleophilic substitution.
- Secondary Haloalkanes: Can undergo both substitution and elimination.
- Tertiary Haloalkanes: Mainly undergo elimination.
